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Abstract:

A prepreg peel ply material (21) to be used for improving the surface
roughness of a composite laminate (13) comprising a backing paper (23)
and a base fabric (27) impregnated with a thermosetting resin, wherein
the adherence between the backing paper (23) and the base fabric (27),
measured by a peeling off parameter P is comprised between 2.9-3.5
min/N/cm2 and the adherence between the base fabric (27) and the
composite material, measured by said parameter P is comprised between
130-160 min/N/cm2. The invention also refers to a method for determining
the adaptability to an ATL machine of a prepreg peel ply material (21)
including the obtention of said parameter P and to a method for
manufacturing a composite component comprising an step of laying-up a
peel ply base fabric (27) with an ATL machine as the last layer of said
component and even as the first layer.

Claims:

1. A method for determining the adaptability to an Automatic Tape Laying
(ATL) machine of a prepreg peel ply material (21) used for improving the
surface roughness of a composite laminate (13) so that it can be
automatically laid-up by said ATL machine, the peel ply material (21)
comprising a backing paper (23) and a base fabric (27) impregnated with a
thermosetting resin, characterized in that it comprises the following
steps: a) providing sheets (31, 33, 35) of, respectively, said backing
paper (23), said base fabric (27) and the composite material; b)
assembling a first sample (41) joining a backing paper sheet (31) and a
base fabric sheet (33) in an overlapping area (32) and a second sample
(43) joining a composite material sheet (35) and a base fabric sheet (33)
in an overlapping area (34) by the application of a vacuum force during a
predetermined time; c) applying tensile forces (F1, F2) in a longitudinal
direction over the edge of the basic fabric sheet (33) of said samples
(41, 43), having its opposed edge fixed to a fixing element (45), up to
the peeling off of the basic fabric sheet (33) from the samples (41, 43)
and measuring the times needed for said peeling off; d) determining said
adaptability of the prepreg peel ply material (21) using a parameter P
setting the relation between said peeling off times, said tensile forces
(F1, F2) and said overlapping areas (32, 34) as a measure of the
adherence between the two elements (31, 33; 35, 33) of said samples (41,
43).

2. The method according to claim 1, wherein: said sheets (31, 33, 35)
have the same dimensions; said overlapping areas (32, 34) extend over a
longitudinal area of said sheets (31, 33; 35, 33) comprised between
10-20% of its total areas; said sample assembling is made applying to
said samples (41, 43) a vacuum force comprised between 400-600 mm of Hg
during a time comprised between 8-12 min.

3. The prepreg peel ply material (21) of claim 1 to be used for improving
the surface roughness of a composite laminate (13), the peel ply material
comprising a backing paper (23) and a base fabric (27) impregnated with a
thermosetting resin, characterized in that: the adherence between the
backing paper (23) and the base fabric (27), measured by the parameter P
is comprised between 2.9-3.5 min/N/cm2; the adherence between the base
fabric (27) and the composite material, measured by the parameter P of
any of claims 1-2, is comprised between 130-160 min/N/cm2.

4. The prepreg peel ply material (21) of claim 2 to be used for improving
the surface roughness of a composite laminate (13), the peel ply material
comprising a backing paper (23) and a base fabric (27) impregnated with a
thermosetting resin, characterized in that: the adherence between the
backing paper (23) and the base fabric (27), measured by the parameter P
is comprised between 2.9-3.5 min/N/cm2; the adherence between the base
fabric (27) and the composite material, measured by the parameter P of
any of claims 1-2, is comprised between 130-160 min/N/cm2.

7. The prepreg peel ply material (21) according to claim 3, wherein said
thermosetting resin is an epoxy resin.

8. The prepreg peel ply material (21) according to claim 4, wherein said
thermosetting resin is an epoxy resin.

9. The prepreg peel ply material (21) according to claim 5, wherein said
thermosetting resin is an epoxy resin.

10. The prepreg peel ply material (21) according to claim 6, wherein said
thermosetting resin is an epoxy resin.

11. The method of claim 3 for manufacturing a composite component
comprising steps of laying-up composite prepreg layers (13) on a mould
(15) using an ATL machine (41), characterized in that also comprise steps
of: a) providing said ATL machine (41) with a prepreg peel ply material
(21) according to claim 3 and laying-up the peel ply base fabric (27)
impregnated with said thermosetting resin as the last layer of said
component; b) curing said composite component and peeling off said peel
ply base fabric (27).

12. The method of claim 4 for manufacturing a composite component
comprising steps of laying-up composite prepreg layers (13) on a mould
(15) using an ATL machine (41), characterized in that also comprise steps
of: a) providing said ATL machine (41) with a prepreg peel ply material
(21) according to claim 4 and laying-up the peel ply base fabric (27)
impregnated with said thermosetting resin as the last layer of said
component; b) curing said composite component and peeling off said peel
ply base fabric (27).

13. The method of claim 5 for manufacturing a composite component
comprising steps of laying-up composite prepreg layers (13) on a mould
(15) using an ATL machine (41), characterized in that also comprise steps
of: a) providing said ATL machine (41) with a prepreg peel ply material
(21) according to claim 5 and laying-up the peel ply base fabric (27)
impregnated with said thermosetting resin as the last layer of said
component; b) curing said composite component and peeling off said peel
ply base fabric (27).

14. The method of claim 6 for manufacturing a composite component
comprising steps of laying-up composite prepreg layers (13) on a mould
(15) using an ATL machine (41), characterized in that also comprise steps
of: a) providing said ATL machine (41) with a prepreg peel ply material
(21) according to claim 6 and laying-up the peel ply base fabric (27)
impregnated with said thermosetting resin as the last layer of said
component; b) curing said composite component and peeling off said peel
ply base fabric (27).

15. The method of claim 7 for manufacturing a composite component
comprising steps of laying-up composite prepreg layers (13) on a mould
(15) using an ATL machine (41), characterized in that also comprise steps
of: a) providing said ATL machine (41) with a prepreg peel ply material
(21) according to claim 7 and laying-up the peel ply base fabric (27)
impregnated with said thermosetting resin as the last layer of said
component; b) curing said composite component and peeling off said peel
ply base fabric (27).

16. The method of claim 8 for manufacturing a composite component
comprising steps of laying-up composite prepreg layers (13) on a mould
(15) using an ATL machine (41), characterized in that also comprise steps
of: a) providing said ATL machine (41) with a prepreg peel ply material
(21) according to claim 8 and laying-up the peel ply base fabric (27)
impregnated with said thermosetting resin as the last layer of said
component; b) curing said composite component and peeling off said peel
ply base fabric (27).

17. The method of claim 9 for manufacturing a composite component
comprising steps of laying-up composite prepreg layers (13) on a mould
(15) using an ATL machine (41), characterized in that also comprise steps
of: a) providing said ATL machine (41) with a prepreg peel ply material
(21) according to claim 9 and laying-up the peel ply base fabric (27)
impregnated with said thermosetting resin as the last layer of said
component; b) curing said composite component and peeling off said peel
ply base fabric (27).

18. The method of claim 10 for manufacturing a composite component
comprising steps of laying-up composite prepreg layers (13) on a mould
(15) using an ATL machine (41), characterized in that also comprise steps
of: a) providing said ATL machine (41) with a prepreg peel ply material
(21) according to claim 10 and laying-up the peel ply base fabric (27)
impregnated with said thermosetting resin as the last layer of said
component; b) curing said composite component and peeling off said peel
ply base fabric (27).

19. The method for manufacturing a component according to claim 11, also
comprising a step of laying-up the peel ply base fabric (27) impregnated
with said thermosetting resin with the ATL machine (41) as the first
layer of said component.

20. The method for manufacturing a component according to claim 12, also
comprising a step of laying-up the peel ply base fabric (27) impregnated
with said thermosetting resin with the ATL machine (41) as the first
layer of said component.

21. The method for manufacturing a component according to claim 13, also
comprising a step of laying-up the peel ply base fabric (27) impregnated
with said thermosetting resin with the ATL machine (41) as the first
layer of said component.

22. The method for manufacturing a component according to claim 14, also
comprising a step of laying-up the peel ply base fabric (27) impregnated
with said thermosetting resin with the ATL machine (41) as the first
layer of said component.

23. The method for manufacturing a component according to claim 15, also
comprising a step of laying-up the peel ply base fabric (27) impregnated
with said thermosetting resin with the ATL machine (41) as the first
layer of said component.

24. The method for manufacturing a component according to claim 16, also
comprising a step of laying-up the peel ply base fabric (27) impregnated
with said thermosetting resin with the ATL machine (41) as the first
layer of said component.

25. The method for manufacturing a component according to claim 17, also
comprising a step of laying-up the peel ply base fabric (27) impregnated
with said thermosetting resin with the ATL machine (41) as the first
layer of said component.

26. The method for manufacturing a component according to claim 18, also
comprising a step of laying-up the peel ply base fabric (27) impregnated
with said thermosetting resin with the ATL machine (41) as the first
layer of said component.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority to pending Spanish Patent
Application No. ES201031718, filed Nov. 23, 2010, the contents of which
are incorporated by reference in its entirety.

FIELD OF THE INVENTION

[0002] The present invention refers to the fabrication of composite
components and more in particular to a peel ply material for use in an
Automated Tape Laying machine and to a composite component fabrication
method where the peel ply is laid-up by an Automated Tape Laying machine.

BACKGROUND OF THE INVENTION

[0003] Composite component manufacturing methods comprising a lay-up stage
where layers of a composite material in a roll format are placed in a
mould of suitable shape and a curing stage are well known in the
aeronautical industry as well as in other industries.

[0004] The composite materials that are most used in the aeronautical
industry consist of fibers or fiber bundles embedded in a matrix of
thermosetting or thermoplastic resin, in the form of a preimpregnated or
"prepreg" material. Their main advantages refer to:

[0005] Their high specific strength with respect to metallic materials.

[0006] Their excellent behavior under fatigue loads.

[0007] The possibilities of structural optimization thanks to the
anisotropy of the material and the possibility of combining fibers with
different orientations, allowing the design of the elements with
different mechanical properties adjusted to the different needs in terms
of applied loads.

[0008] The layers of composite material are not placed randomly, but are
arranged in each zone in a number and with an orientation of their fibre
reinforcement, typically of carbon fibre, that depend on the nature and
the magnitude of the stresses that are to be withstood by the component
in each zone. Thus, each zone has a particular structure of the
arrangement or stacking of the layers. The difference in thickness
between the different zones generates drop-offs in the layers, which
requires having a ply model for each component establishing how to the
arrange the layers on the jig during the stacking process. The final
result is a laminate (flat or with curvature) with zones of different
thickness.

[0009] The lay-up stage is usually carried out, particularly for large
components such as the skins of aircraft wings, using Automatic Tape
Laying machines (hereinafter ATL machines) for laying unidirectional (UD)
or fabric tapes.

[0010] Before the curing stage is carried out in an autoclave with
temperature and vacuum until the component reaches its finished state, a
peel ply material, such as a textured fabric, is applied over the upper
layer (in some specific cases could also be laid up as the first ply) of
the composite material to provide the surface of the component with the
appropriate roughness for facilitating the union of additional elements
such as stringers to aircraft wing skins or superficial coatings. After
the curing stage the peel ply material is peeled off leaving a textured
surface in the composite component.

[0011] A peel ply is then a high drapable fabric, usually made of nylon,
used to acquire the proper texture on the surface of a composite
laminate. The peel-ply surface is helpful for secondary bonding or
painting the component, avoiding the need of sanding. The fabric is
treated in such a way to prevent shrinkage and to remove contaminates.

[0012] A preimpregnated peel-ply (hereinafter prepeg peel-ply) is made of
the fabric previously mentioned embedded in a resin matrix.

[0013] In the prior art, the prepreg peel ply is placed manually as the
first and/or last layer of the laminate. In the case of composite
components that includes curved sectors, such as an aircraft wing skin of
a large dimension, the prepreg peel ply lay-up task is therefore a very
labour consuming task.

[0014] It would be thus desirable a composite component fabrication method
where the peel ply be laid-up by an automated tape laying machine.

SUMMARY OF THE INVENTION

[0015] An object of the present invention is to provide a method for
determining the adaptability of a prepreg peel ply material used for
improving the surface roughness of a composite laminate to an ATL machine
so that it can be automatically laid-up by said ATL machine.

[0016] Another object of the present invention is to provide a prepreg
peel ply material used for improving the surface roughness of a composite
laminate able to be laid-up by an ATL machine.

[0017] Another object of the present invention is to provide a composite
component fabrication method where the prepeg peel ply is laid-up by an
ATL machine.

[0018] In one aspect these and another objects are met by a method for
determining the adaptability to an ATL machine of a prepreg peel ply
material used for improving the surface roughness of a composite laminate
so that it can be automatically laid-up by said ATL machine, the prepeg
peel ply material comprising a backing paper and a base fabric
impregnated with a thermosetting resin, that comprises the following
steps:

[0020] b) assembling a first sample joining a backing paper sheet and a
base fabric sheet in an overlapping area and a second sample joining a
composite material sheet and a base fabric sheet in an overlapping area
by the application of a vacuum force during a predetermined time;

[0021] c) applying tensile forces F1, F2 in a longitudinal direction over
the edge of the basic fabric sheet of said samples, having its opposed
edge fixed to a fixing element, up to the peeling off of the basic fabric
sheet from the samples and measuring the times needed for the peeling
off;

[0022] d) determining said adaptability of the prepreg peel ply material
using a parameter P setting the relation between said peeling off times,
said tensile forces F1, F2 and said overlapping areas as a measure of the
adherence between the two elements of said samples.

[0023] In a preferred embodiment, said sheets have the same dimensions,
said overlapping areas extend over a longitudinal area of said sheets
comprised between 10-20% of its total areas and said sample assembling is
made applying to said sheets a vacuum force comprised between 400-600 mm
of Hg during a time comprised between 8-12 min. Hereby it is achieved a
suitable method for the peel ply material used in the fabrication of
composite components particularly in the aeronautical industry.

[0024] In another aspect the above-mentioned objects are met by a prepreg
peel ply material comprising a backing paper and a base fabric
impregnated with a thermosetting resin in which the adherence between the
backing paper and the base fabric measured by the above-mentioned
parameter P, is comprised between 2.9-3.5 min/N/cm2 and the adherence
between the base fabric and the composite material, measured by the
above-mentioned parameter P, is comprised between 130-160 min/N/cm2.

[0025] In a preferred embodiment the base fabric is nylon having the
impregnated thermosetting resin (preferably epoxy resin) symmetrically
distributed. Hereby it is achieved a suitable peel ply material for being
used in the fabrication of composite components using ATL machines.

[0026] In another aspect the above-mentioned objects are met by a method
for manufacturing a composite component comprising steps of laying-up
composite prepreg layers on a mould using an ATL machine, that also
comprise steps of:

[0027] a) providing said ATL machine with the above-mentioned prepreg peel
ply material and laying-up the peel ply base fabric impregnated with said
thermosetting resin as the last layer of said component and, if required,
also as the first layer;

[0029] Other characteristics and advantages of the present invention will
be clear from the following detailed description of embodiments
illustrative of its object in relation to the attached figures.

DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 shows a schematic perspective view of the lay-up of a
composite component.

[0031] FIG. 2 shows a schematic sectional view of a prepreg peel ply layer
according to the present invention.

[0032] FIG. 3 shows schematically the arrangement of two samples used in
the method for determining the adaptability to an ATL machine of a
prepreg peel ply material according to this invention and FIG. 4 shows
schematically the application of tensile forces to said two samples.

[0033] FIG. 5 is a schematic view of the lay-up of the prepreg peel ply
layer of a composite component using an ATL machine.

DETAILED DESCRIPTION OF THE INVENTION

[0034] Automated procedures for the lay-up stage in composite component
manufacturing methods, particularly for large components such as aircraft
wing skins, are well known in the art. ATL machines have a movable tape
delivery head mechanism mounted between parallel guides that can be moved
along multiple axis to place a prepreg tape on a variety of mould shapes.
The prepreg tape, usually provided in a large roll format, contains
uncured composite material held on a backing paper which is removed as
the tape is placed on the mould.

[0035] In the prior art, it is considered that a prepreg peel ply 21 (see
FIG. 1) can not be placed using an ATL machine on a composite laminate 13
laid-up by an ATL machine over a mould 15 because an adequate prepreg
peel-ply format had not been achieved yet.

[0036] In fact, the inventors have tested a typical prepreg peel ply used
in the aeronautical industry such as Hexcel's F161/43%/F0811, composed by
a nylon fabric and a thermosetting resin where a backing paper was added
in order to obtain a product in ATL format. It was verified that this
material can not be laid-up using an ATL machine due to, on the one hand,
an excess of adherence between the backing paper and the prepreg peel ply
and, on the other hand, to the resin transference to the ATL machine
guides.

[0037] There are a big number of prepreg peel ply features to be
considered for finding a suitable prepreg peel ply to be laid-up with an
ATL machine such as, particularly, the following: [0038] Type of fabric
(nylon, polyester, . . . ). [0039] Type of resin, resin content (%),
resin distribution (symmetric or asymmetric), impregnation level. [0040]
Type of backing paper, paper release properties.

[0041] The backing paper of said prepreg peel ply material shall have
sufficient dimensional stability, tear strength and burst strength to
withstand the many forces that are applied to the backing paper as it
travels through the ATL machine guides. The backing paper must also be
resistant to moisture for dimensional stability purposes and in order to
prevent possible water-based degradation of the backing paper when it is
in storage, in use and under tension. Paper-based backing materials,
which have been treated with silicone as a release agent, are commonly
used for automated tape laying machines with prepreg tapes but the peel
ply base fabric has very different release requirements than the backing
paper usually used in other prepreg materials.

[0042] In particular, the prepreg peel ply material shall avoid:

[0043] An excessive adherence between the backing paper and the resin
impregnated fabric.

[0044] That the ATL machine guides be impregnated with resin for allowing
correct sliding of the prepreg peel ply.

[0045] A resin transfer from the prepreg peel ply to the backing paper.

[0046] As the prior art does not provide any information for solving the
above mentioned problem the inventors have developed a method for
determining the adaptability to an ATL machine of a prepreg peel ply
material 21 comprising (see FIG. 2) a backing paper 23 with an inner
coating 25 of a release material and a base fabric 27 impregnated with a
thermosetting resin.

[0047] The method is based on the consideration that the main properties
of the peel ply material involved in this problem are:

[0048] The release of the backing paper 23 to the extend that it appears
to be a relevant property regarding the adherence between the backing
paper 23 and the base fabric 27.

[0049] The tacking of the base fabric 27 to the extend that it appears to
be relevant a property regarding the adherence between the base fabric 27
and the composite laminate 13.

[0052] b) Assembling a first sample 41 joining a backing paper sheet 31
and a base fabric sheet 33 in an overlapping area 32 and a second sample
43 joining a composite material sheet 35 and a base fabric sheet 33 in an
overlapping area 34 by the application of a vacuum force during a
predetermined time.

[0053] c) Applying tensile forces F1, F2 in a longitudinal direction over
the edge of the basic fabric sheet 33 of said samples 41, 43, having its
opposed edge fixed to a fixing element 45 up to the peeling off of the
basic fabric sheets 33 from the samples 41, 43 (i.e from, respectively,
the backing paper 31 and the composite material 35) and measuring the
times needed for said peeling off. As the skilled man will easily
understand the steps a), b), c) will be repeated in a suitable number of
times to provide reliable results.

[0054] d) Determining said adaptability of the prepreg peel ply material
21 using a parameter P setting the relation between said peeling off
times, said tensile forces F1, F2 and said overlapping areas 32, 34 as a
measure of the adherence between the two elements 31, 33; 35, 33 of said
samples 41, 43.

[0055] In a preferred embodiment said sheets 31, 33, 35 have the same
dimensions, said overlapping areas 32, 34 extend over a longitudinal area
of said sheets 31, 33; 35, 33 comprised between 10-20% of its total areas
and said sample assembling is made applying to said samples 41, 43 a
vacuum force comprised between 400-600 mm of Hg during a time comprised
between 8-12 min.

[0056] In a particular example the following values of the above mentioned
parameters were used:

[0057] The length L of all said sheets 31, 33, 35 was 210 mm and the width
W of all of said sheets 31, 33, 35 was 150 mm.

[0058] The overlapping areas 32, 34 had a length L1 of 30 mm.

[0059] A vacuum force of 500 mm of Hg was applied during 10 minutes.

[0060] A force of 10 N was applied to the sample 41 joining a backing
paper sheet 31 and a base fabric sheet 33.

[0061] A force of 45 N was applied to the sample 43 joining a composite
material sheet 35 and a base fabric sheet 33.

[0062] Using said method the inventors found that a prepeg peel ply
material 21 is able for being used by an ATL machine when:

[0063] The parameter P obtained for said first sample 41 is comprised
between 2.9-3.5 min/N/cm2.

[0064] The parameter P obtained for said second sample 43 is comprised
between 130-160 min/N/cm2.

[0065] In these conditions the backing paper 23 has the appropriate
adherence for, on the one hand, keeping the peel ply material stuck
before being used in an ATL machine and, on the other hand, for allowing
a correct release between itself and the base fabric 27 when is laid-up
with an ATL machine, and the base fabric 27 has the appropriate resin
content for, on the one hand, allowing a correct sliding of the prepreg
peel ply material 21 in and ATL machine, and on the other hand, for
avoiding a resin transfer to the backing paper 23.

[0066] In a preferred embodiment, said base fabric 27 is a nylon fabric
having the thermosetting resin symmetrically distributed.

[0067] In another preferred embodiment said thermosetting resin is an
epoxy resin.

[0068] A method for manufacturing a composite component according to the
present invention (see FIGS. 1 and 5) comprises steps of:

[0069] a) Laying-up the composite prepreg layers 13 on a mould 15 using an
ATL machine 41, as in the prior art.

[0070] b) Providing said ATL machine 41 with a prepreg peel ply material
21 with the above-mentioned features and using said ATL machine 41 for
laying-up the peel ply base fabric 27 impregnated with said thermosetting
resin as the last layer of the component.

[0072] The method can also include an step for laying-up the peel ply base
fabric 27 impregnated with said thermosetting resin as the first layer.

[0073] The prepeg peel ply material 21, wound in a roll format, is loaded
in the ATL machine 41, then the backing paper 23 is separated and rewound
in the rewinder 45 and the base fabric 27, fed through the guides 47, is
laid-up as the first and/or the last layer of the laminate 13.

[0074] Said first layer is applied to those components needing specific
finishing features in its outer surface. Said last layer is applied to
those components to which additional elements shall be joined on its
inner surface such as the stringers joined to an aircraft wing skin.

[0075] Among the advantages of the present invention, the following can be
highlighted:

[0077] Quality improvement. The method according to the present invention
assures a much better positioning accuracy while avoiding the typical
wrinkles that are usually present in the manual placement.

[0078] No additional machines are required. The peel-ply configuration has
been developed in such a way that standard ATL machines can be used for
its automatic placement.

[0079] Better ergonomics. Workforce has no longer the need neither to bend
down nor to step on the surface tool.

[0080] Although the present invention has been fully described in
connection with preferred embodiments, it is evident that modifications
may be introduced within the scope thereof, not considering this as
limited by these embodiments, but by the contents of the following
claims.

Patent applications by AIRBUS Operations S.L.

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